Abstract
Historically, the first fundamental idea for a theory of nuclear forces was advanced by the Japanese physicist Hideki Yukawa in 1935. He proposed that the exchange of subnuclear particles (eventually called mesons) between nucleons would create the force. The resulting meson theory was the most popular approach to nuclear forces for more than half a century. However, with the advancement of quantum chromodynamics (QCD) to the fundamental theory of strong interactions, meson theory had to be demoted to the level of a model. Yet, among all approaches to the nuclear force, the meson model remains the most insightful as well as the most quantitative one. Nucleon-nucleon potentials based upon meson-exchange are still today in frequent use. Because of its historical and conceptual value as well as its quantitative strength, the meson model is discussed in detail in this chapter. Since meson theory and phenomenology have been entwined throughout history, we also review the phenomenological approach to nuclear forces.